Q: Is this mushroom something to be concerned about? Age of the tree is unknown. It was left when the land was cleared for the house in early 90’s and stands about 12 feet from the house foundation.
A: The mushroom at the base of the tree is an indicator of rot within the tree trunk. My bet is that when the land was cleared a lot of soil was pushed around the base of the tree. The trunk began to rot as a result.
The trunk looks like a telephone pole coming out of the ground, I don’t see the big flare that would be expected where the trunk divides into roots.
You need to hire an ISA certified arborist to take a look. I am guessing they will recommend the tree needs to come down.